Below are the 2 simple steps on how you can add this menu to your blogger blog.

Step 1 : Adding the CSS

First go to Blog Title → Template → Edit HTML. Press Ctrl + F. Expand
<b:skin>...</b:skin> if it is not expanded. Type ]]></b:skin> in search box and press enter key. [As per the new HTML editor]
Add the below given code just above ]]></b:skin>